The population incidence of IR is estimated to be as high as 10%. The pathophysiology of IR is largely unknown. Several hypotheses have been put forward. In general it is assumed that neurogenic mechanisms play an important role. Neuropeptides like CGRP, SP, NKA/B, NPY, NGF are released from afferent neurons in the nasal mucosa after activation by unspecific stimuli and can be responsible for the symptoms of IR.